The present invention relates to a water soluble dyestuff for inkjet recording, an aqueous inkjet recording liquid comprising the water soluble dyestuff and an inkjet recording method using the aqueous inkjet recording liquid. More particularly, the invention relates to a metal chelated dyestuff comprising a water soluble azo metal chelated compound suitable for inkjet recording, an aqueous inkjet recording liquid comprising the metal chelated dyestuff and an inkjet recording method using the aqueous inkjet recording liquid.
A so-called inkjet recording method which allows droplets of a recording liquid containing water soluble dyes such as direct dye and acidic dye to be ejected from a minute ejection orifice to effect recording has been put to practical use.
The recording liquid requires that it be fixed rapidly on recording paper widely used for general official purposes such as PPC (plain paper COPIA) paper such as electrophotographic paper and fanhold paper (continuous paper for computer, etc.) and give a printed matter having a good print quality, i.e., print having a definite contour free of running. The recording liquid further requires that it exhibit an excellent storage stability as a recording liquid. Accordingly, the solvent which can be used in the recording liquid is remarkably limited.
Further, the dye for recording liquid requires that it have a sufficient solubility in the solvent thus restricted and remain stable even after prolonged storage in the form of recording liquid. The dye for recording liquid also requires that it give a printed image having high saturation and density and an excellent water resistance, light-fastness and indoor discoloration resistance.
In order to form a full-color image by an inkjet recording method, inks of three primary colors, i.e., yellow (Y), magenta (M) and cyan (C) or inks of four colors, including black (Bk) added thereto, are ejected onto a recording material in a controlled amount so that these inks are mixed to form an image. In order to form such a full-color image, it is necessary to express not only difference in color but also color density. The dark and light colored area is normally formed by two or more inks having different dyestuff concentrations.
However, the conventional inkjet recording dyestuffs are disadvantageous in that they are poor in resistance to discoloration under light, i.e., light-fastness, particularly on a light-colored area formed by an ink having a low dyestuff concentration.
In particular, as magenta dyestuffs to be incorporated in the recording liquid there have heretofore been used metal-free direct dyes (C.I. DR-227) or acidic dyes (C.I. AR-249), which are commercially available (The term xe2x80x9cC.I.xe2x80x9d stands for xe2x80x9ccolor indexxe2x80x9d, the term xe2x80x9cARxe2x80x9d stands for xe2x80x9cacid redxe2x80x9d, and the term xe2x80x9cDRxe2x80x9d stands for xe2x80x9cdirect redxe2x80x9d.). However, the direct dyes have an unclear color tone. On the contrary, acidic dyes having a sharp color tone tend to have a deteriorated light-fastness. Further, the conventional metal-containing azo-based dyestuffs have a good light-fastness but have a blurred and unclear color tone.
Japanese Patent Laid-Open No. 1982-42775 discloses an aqueous ink for inkjet printing comprising at least one 5-hydroxypyrazole azo dye having an azo group in the 4-position or complex salt dye thereof with copper, nickel or cobalt. Japanese Patent Laid-Open No. 1998-259331 discloses an aqueous inkjet recording liquid comprising a water soluble complex formed by a benzene azo compound and at least one metal selected from nickel, cobalt, chromium and copper. Further, Japanese Patent Laid-Open No. 1999-140367 discloses an ink composition comprising a magenta dye ligand of 4-hydrox-3-(2xe2x80x2-pyridylazo)-1-(sulfo-substituted)-naphthalene having polyvalent metal ions coordinated therein and an ink vehicle.
However, these dyestuffs do not necessarily meet requirements for sharpness of color tone, light-fastness, indoor discoloration resistance, solubility, storage stability, etc. for use in inkjet recording.
Among the metals to be incorporated in the metal chelated compound, copper is cheaper than nickel, cobalt, etc. and is desired in safety. However, any of conventional metal chelated dyestuffs for inkjet recording comprising copper incorporated therein as a metal has left something to be desired in saturation.
An aim of the invention is to provide a metal chelated dyestuff for inkjet recording which provides a recorded image having a good print quality, a sharp color tone, a high density and an excellent light-fastness and showing little indoor discoloration even when subjected to inkjet recording on ordinary paper and exhibits a good dyestuff solubility and a good dyestuff stability after prolonged storage, an aqueous inkjet recording liquid comprising the metal chelated dyestuff and an inkjet recording method using the aqueous inkjet recording liquid.
Another aim of the invention is to provide a metal chelated dyestuff for inkjet recording sufficiently excellent in properties such as saturation, print density, light-fastness, indoor discoloration resistance and storage stability even when it comprises copper incorporated therein as a metal element, an aqueous inkjet recording liquid comprising the metal chelated dyestuff and an inkjet recording method using the metal chelated dyestuff.
The metal chelated dyestuff for inkjet recording of the invention is a water soluble azo metal chelated compound formed by an azo-based compound represented by the following general formula (1) having one or more hydrophilic group per molecule and a metal element.
The metal chelated dyestuff for inkjet recording of the invention is a water soluble azo metal chelated compound formed by an azo-based compound the free acid form of which is represented by the following general formula (1) and having one or more hydrophilic group per molecule and a metal element. 
wherein X1 represents a chain of a plurality of atoms containing a total of 2 or more hetero atoms of one or more kinds selected from the group consisting of nitrogen atom, oxygen atom and sulfur atom and required to form at least one 5- to 7-membered heterocyclic ring; the heterocyclic ring containing X1 may have substituents thereon; the substituents on the heterocyclic ring may further be condensed to form a condensed ring; the condensed heterocyclic ring containing X1 may be substituted, with the proviso that the heterocyclic ring containing X1 is not a heterocyclic ring represented by the following general formula (2) or (3); and Ar1 represents naphthyl group represented by any one of the following general formulae (4) to (6): 
wherein R represents hydrogen atom or arbitrary substituent; 
wherein Y1 represents a chelating group; Z1""s represent arbitrary substituents which may be different from each other; and a represents an integer of from 0 to 6.
The aqueous inkjet recording liquid of the invention comprises an aqueous medium and one or more metal chelated dyestuffs for inkjet recording of the invention.
The inkjet recording method of the invention involves the use of such an aqueous inkjet recording liquid of the invention.
In other words, the inventors found that a water soluble dyestuff comprising a water soluble azo metal chelated compound of the aforementioned azo-based compound or a compound the free acid form of which is the aforementioned azo-based compound with a metal element can accomplish the aforementioned aim and thus worked out the invention.
The reason why the metal chelated compound of specific azo-based compound represented by the aforementioned general formula (1) is comprehensively excellent in print density, light-fastness, indoor discoloration resistance, storage stability, etc. as an inkjet recording dyestuff is unknown. However, it is presumed that the connection of the specific skeleton of the azo-based compound to diazo group causes the formation of a stable chelate with a metal without deteriorating solubility, providing a high saturation dyestuff.
Further, the metal chelated dyestuff of the invention is sufficiently excellent in saturation, print density, light-fastness, indoor discoloration resistance, storage stability, etc. even when it comprises copper, which is inexpensive and preferable in safety, incorporated therein as a metal element, and thus has an extremely high industrial value.